CH. VII.] LUMINOUS WINGED INSECTS. 123 



infers that the luminous matter in the glow-worm is 

 absorbed, being replaced by the interstitial matter, 

 when the season for emitting light is gone by. He 

 also observed two minute elliptical sacs, formed of 

 an elastic fibre, wound spirally, and similar to that 

 of the tracheae of insects, which contained a yellow 

 substance, soft in consistency, and closer in texture 

 than that lining the adjoining region, and affording 

 a more brilliant and permanent light. This light he 

 concluded to be less under the control of the in- 

 sect than the luminous substance in its vicinity, 

 which he infers it has the property voluntarily to 

 extinguish, referable to some inscrutable power de- 

 pendant on volition, and not, as was advocated by 

 Carradori, by retracting it under a membrane : when 

 he extracted the latter from living glow-worms it 

 afforded no light, while the two sacs, in like circum- 

 stances, shone uninterruptedly for several hours. 



It was supposed by Dr. Darwin that the luminous 

 appearance was owing to a secretion of some phos- 

 phoric matter, and a slow combustion arising from 

 this phosphorus entering into combination with the 

 oxygen inspired ; Mr. Murray, however, has experi- 

 mentally ascertained. "that the luminous matter 

 does not contain phosphorus." It was, however, 

 regarded by Spallanzani as a compound of hydrogen 

 and phosphoretted hydrogen: this gentleman and 

 Foster also ascertained that the luminous matter 

 shone more brilliantly in oxygen : yet several ex- 

 perimenters have found no such effect take place. 

 It has also been stated, that the light of the glow- 

 worm is extinguished by the application of hydro- 

 gen and carbonic acid gas ; while, on the other 

 hand, these effects have also been contradicted ; but 

 it is added, that the insect appears not to suffer ma- 

 terially in the former; and though the insect ex- 

 pired in carbonic acid gas, the light suffered no 

 eclipse by its death, but continued for some time. 



It has also been stated, that the light was in- 



